In e.g. industrial trucks there are mechanical constructions that interact with hydraulic cylinder assemblies, where the interacting motion of the mechanics is not accurate. There is always a force for returning the piston rod back into the cylinder and the force can be the weight from the load that is intended to be lifted by the piston rod of the hydraulic cylinder. The forces from the mechanics of the industrial truck are sometimes not applied to the piston rod in the centre axis of the cylinder. This results in an obliqueness of the piston rod relative the cylinder. An out-of-line force causes a moment and an inclination of the piston rod that result in side forces and a high contact pressure between the piston rod and the cylinder. Although there have been attempts to eliminate the effects of out-of-line forces in a hydraulic cylinder assembly by providing a cylinder pipe that is accurately turned out, such that the piston rod travels in the cylinder with a minimal gap to the inner wall of the cylinder, there will still be a play between the rod and the cylinder. As a result, out-of-line force causes an inclination of the piston rod that result in high contact pressure between the piston rod and the cylinder, which may give rise to scratching of the piston rod by the cylinder inner wall. There are a number of further drawbacks with such a machined cylinder pipe, relating to the design of the system, such as the amount of lubricating film of hydraulic oil in the contact area, surface contact forces, undefined forces and point forces, as well as pressure build-up.
In recent years, the problems mentioned above have been solved by providing guide rings for rods and piston guides in hydraulic cylinders. U.S. Pat. No. 6,012,847 discloses guide-ring arrangements for hydraulic cylinder. However, guide rings require some space in the cylinder. The guide rings are expensive and subjected to wear.